Al-Mg-Si Alloy Exhibiting Superior Combination of Strength and Energy Absorption

ABSTRACT

The present invention relates to an aluminum 6XXX (Al—Mg—Si) alloy extrusion component exhibiting a superior combination of strength and energy absorption for crash management applications in automotive markets and for other applications where energy absorption is a critical property. These components provide yield strengths greater than 260 MPa, and preferably greater than 280 MPa, while simultaneously providing energy absorption per unit cross-sectional area of greater than 20 kJ/mm 2  using the defined crush testing parameters in the present specification.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit, under 35 USC 119(e), of U.S.Provisional Application No. 62/872,384 filed Jul. 10, 2019, the contentsof which are incorporated herein by reference.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention generally related to an improved aluminum 6XXXalloy extrusion component with high strengths and energy absorption.

Background

The automotive industry is continuously looking at means to lightweightcomponents in an effort to improve fuel efficiency and meet CAFE(corporate average fuel economy) standards. Simultaneously there is adesire to continuously improve the safety rating of the vehicle withdesigns and materials that absorb the energy from a crash withouttransmitting it to the driver or passengers. Aluminum extrusions havebeen used to achieve these goals for years, but lower strength alloyshad to be utilized in certain applications where energy absorptionwithout fracture of the material was required. Higher strength aluminumalloys enable additional fuel efficiency improvements in theseapplications by allowing thinner sections with reduced cross sectionalareas. These alloys, properly processed, provide the energy absorptionand fracture performance necessary to attain safety requirements.

SUMMARY OF INVENTION

The present invention is an improved aluminum 6XXX alloy extrusioncomponent with high strengths and energy absorption produced from analloy composition including, in weight percent, Si: 0.50-0.80; Fe:<0.40; Cu: 0.15-0.35; Mn: 0.20-0.50; Mg: 0.50-0.80; Cr: 0.10-0.25; Zn:<0.20; with other elements being considered incidental impurities andconsisting of less than 0.05 individually and 0.15 in total with thebalance being aluminum. In a preferred embodiment, the alloy compositiondoes not require any additions of vanadium, thus reducing cost and alsopreventing contamination of the recycling scrap stream.

BRIEF DESCRIPTION OF THE DRAWINGS

The features and advantages of the present invention will becomeapparent from the following detailed description of a preferredembodiment thereof, taken in conjunction with the accompanying drawings,in which:

FIG. 1 shows a three void hollow extrusion design including the alloycomposition of the present invention;

FIG. 2 is a photo showing the comparison of microstructures with thinperipheral coarse grain band on the left being acceptable (cast 78 fromExample 1) and the thick coarse grain band on the right beingunacceptable (cast 77 from Example 1);

FIG. 3 is a photo showing rough deformed surface (orange peel) ofmaterial with coarse recrystallized grains;

FIG. 4 is a photo showing smooth deformed surface of material withminimal coarse recrystallized grains;

FIG. 5 is a graph showing the specific energy absorption along theextruded length (data from Example 2);

FIG. 6 is a graph showing the relationship between yield strength andspecific energy absorption (data from Example 4);

FIG. 7 is a graph showing the relationship between yield strength andspecific energy absorption and Mg+Si (data from Example 4); and

FIG. 8 is a graph showing the relationship between yield strength andspecific energy absorption and Mg+Si+Cu (data from Example 4).

DETAILED DESCRIPTION OF THE INVENTION

The present invention is an aluminum 6XXX alloy extrusion componentproduced from an alloy composition comprising, optionally consistingessentially of, or optionally consisting of, in weight percent (wt. %):Si: 0.50-0.80; Fe: <0.40; Cu: 0.15-0.35; Mn: 0.20-0.50; Mg: 0.50-0.80;Cr: 0.10-0.25; Zn: <0.20; with other incidental elements beingconsidered impurities and consisting of less than 0.05 individually and0.15 in total with the balance being aluminum. In one embodiment of thepresent invention, the alloy composition does not include anyintentional additions of vanadium. In one embodiment, the alloycomposition includes ≤0.04 wt. % vanadium. It should be understood thatthe recitation of a range of values includes all of the specific valuesin between the highest and lowest value.

Silicon is included in the alloy composition of the present invention inthe range of 0.50 to 0.80 wt. %. It is understood that within the rangeof 0.50 to 0.80 wt. % Si, the upper or lower limit for the amount of Simay be selected from 0.50, 0.51, 0.52, 0.53, 0.54, 0.55, 0.56, 0.57,0.58, 0.59, 0.60, 0.61, 0.62, 0.63, 0.64, 0.65, 0.66, 0.67, 0.68, 0.69,0.70, 0.71, 0.72, 0.73, 0.74, 0.75, 0.76, 0.77, 0.78, 0.79, and 0.80 wt.% Si.

In addition to the amounts of silicon provided above, iron may beincluded in the alloy composition of the present invention in an amountthat is <0.40 wt. %. It is understood that within the range of <0.40 wt.%, the upper or lower limit for the amount of Fe may be selected from0.40, 0.39, 0.38, 0.37, 0.36, 0.35, 0.34, 0.33, 0.32, 0.31, 0.30, 0.29,0.28, 0.27, 0.26, 0.25, 0.24, 0.23, 0.22, 0.21, 0.20, 0.19, 0.18, 0.17,0.16, 0.15, 0.14, 0.13, 0.12, 0.11, 0.10, 0.09, 0.08, 0.07, 0.06, 0.05,0.04, 0.03, 0.02, and 0.01 wt. %.

In addition to the amounts of silicon and iron provided above, coppermay be included in the alloy composition of the present invention in therange of 0.15-0.35 wt. %. It is understood that within the range of0.15-0.35 wt. %, the upper or lower limit for the amount of Cu may beselected from 0.35, 0.34, 0.33, 0.32, 0.31, 0.30, 0.29, 0.28, 0.27,0.26, 0.25, 0.24, 0.23, 0.22, 0.21, 0.20, 0.19, 0.18, 0.17, 0.16, and0.15 wt. %.

In addition to the amounts of silicon, iron, and copper provided above,manganese may be included in the alloy composition of the presentinvention in the range of 0.20-0.50 wt. %. It is understood that withinthe range of 0.20-0.50 wt. %, the upper or lower limit for the amount ofMn may be selected from 0.50, 0.49, 0.48, 0.47, 0.46, 0.45, 0.44, 0.43,0.42, 0.41, 0.40, 0.39, 0.38, 0.37, 0.36, 0.35, 0.34, 0.33, 0.32, 0.31,0.30, 0.29, 0.28, 0.27, 0.26, 0.25, 0.24, 0.23, 0.22, 0.21, and 0.20 wt.%.

In addition to the amount of silicon, iron, copper, and manganeseprovided above, magnesium may be included in the alloy composition ofthe present invention in the range of 0.50 to 0.80 wt. %. It isunderstood that within the range of 0.50 to 0.80 wt. % Mg, the upper orlower limit for the amount of Mg may be selected from 0.50, 0.51, 0.52,0.53, 0.54, 0.55, 0.56, 0.57, 0.58, 0.59, 0.60, 0.61, 0.62, 0.63, 0.64,0.65, 0.66, 0.67, 0.68, 0.69, 0.70, 0.71, 0.72, 0.73, 0.74, 0.75, 0.76,0.77, 0.78, 0.79, and 0.80 wt. %.

In addition to the amounts of silicon, iron, copper, manganese, andmagnesium provided above, chromium may be included in the alloycomposition of the present invention in the range of 0.10-0.25 wt. %. Itis understood that within the range of 0.10-0.25 wt. %, the upper orlower limit for the amount of Cr may be selected from 0.25, 0.24, 0.23,0.22, 0.21, 0.20, 0.19, 0.18, 0.17, 0.16, 0.15, 0.14, 0.13, 0.12, 0.11,and 0.10 wt. %.

In addition to the amounts of silicon, iron, copper, manganese,magnesium, and chromium provided above, zinc may be included in thealloy composition of the present invention in an amount that is <0.20wt. %. It is understood that within the range of <0.20 wt. %, the upperor lower limit for the amount of Zn may be selected from 0.20, 0.19,0.18, 0.17, 0.16, 0.15, 0.14, 0.13, 0.12, 0.11, 0.10, 0.09, 0.08, 0.07,0.06, 0.05, 0.04, 0.03, 0.02, and 0.01 wt. %.

In addition to the amounts of silicon, iron, copper, manganese,magnesium, chromium, and zinc provided above, it is understood thatvanadium is not intentionally added to the alloy composition of thepresent invention. Vanadium may exist in the alloy composition of thepresent invention as a result of a non-intentionally added element. Inone embodiment, the alloy composition of the present invention includes≤0.04 wt. % vanadium. It is understood that within the range of <0.04wt. %, the upper or lower limit for the amount of V may be selected from0.04, 0.03, 0.02, 0.01, and 0.005 wt. %

In addition to the amounts of silicon, iron, copper, manganese,magnesium, chromium, zinc, and vanadium, Sn may be intentionally addedwithin the range of 0.02-0.10% by weight to improve adhesive bonddurability performance. It is understood that within the range of0.02-0.10 wt. %, the upper or lower limit for the amount of Sn may beselected from 0.10, 0.09, 0.08, 0.07, 0.06, 0.05, 0.04, 0.03, and 0.02wt. %.

In addition to the amounts of silicon, iron, copper, manganese,magnesium, chromium, zinc, vanadium, and tin, Sr may be intentionallyadded within the range of up to 0.30% by weight. It is understood thatwithin the range of up to 0.30 wt. %, the upper or lower limit for theamount of Sr may be selected from 0.30, 0.29, 0.28, 0.27, 0.26, 0.25,0.24, 0.23, 0.22, 0.21, 0.20, 0.19, 0.18, 0.17, 0.16, 0.15, 0.14, 0.13,0.12, 0.11, 0.10, 0.09, 0.08, 0.07, 0.06, 0.05, 0.04, 0.03, 0.02, and0.01 wt. %.

The alloy composition of the present invention may also include lowlevel of “incidental elements” that are not included intentionally. The“incidental elements” means any other elements except the abovedescribed Al, Si, Fe, Cu, Mn, Mg, Cr, Zn, Sn, Sr and V.

The alloy composition may be used to produce an automotive crush can,front rail, rear rail, upper rail, rocker, header, A-pillar, or roofrail.

The extrusion component may be produced by i) homogenizing a billetincluding the present alloy composition at a billet temperature between527-566° C., ii) followed by fan cooling, iii) followed by either a)extruding at a billet temperature of 455° C. to 510° C. orb) heating toa billet temperature of 491° C.-535° C., then water quenching to abillet temperature of 388° C.-496° C., and then extruding, and iv)followed by cold water quenching, stretching and artificial aging withthe extrusion component having a specific energy absorption of greaterthan 22 kJ/mm² and a yield strength of greater than 260 MPa, or 280 MPa,while providing no fragmentation or surface cracks greater than 10 mmduring defined crush testing (as defined herein). In an alternateembodiment, the end product has a specific energy absorption of greaterthan 22 kJ/mm² and a yield strength of greater than 280 MPa, whileproviding no fragmentation or surface cracks greater than 20 mm duringdefined crush testing (as defined herein). In another alternateembodiment, the end product has a specific energy absorption of greaterthan 22 kJ/mm² and a yield strength of greater than 300 MPa, whileproviding no fragmentation or surface cracks greater than 30 mm duringdefined crush testing (as defined herein). The superior combination ofstrength and energy absorption for crash management applications is abasic and novel characteristic of the present invention.

The crash worthiness of an automotive component is typically assessed bythe amount of energy absorbed in a crush test, without having anyunacceptable fracturing of the component. “Crush testing” as used hereinis conducted by taking a 300 mm long sample and crushing in thelongitudinal direction to 100 mm at a rate of 100 mm/minute. The forcerequired through the stroke of the crush testing is recorded and thearea under the force displacement curve is the energy absorption. Oncethe crush testing is complete, the sample is visually examined forfractures and surface cracking. Fractures resulting in fragmentation arenot acceptable and surface cracks are not desirable, but may beacceptable for certain applications provided they are not too severe.Surface cracks are typically limited to a maximum observable length,perhaps 10 mm, or 20 mm, or 30 mm. For some applications longer surfacecracks may be deemed acceptable with a corresponding increase in yieldstrength or energy absorption. A sample that does not pass the visualexamination, however, is considered a failed sample, regardless of theenergy absorbed. Thus the visual examination is a binary, pass/failassessment. Samples passing the visual examination can thus be comparedquantitatively relative to the energy absorption. This is the crushtesting basis for all results reported herein.

Energy absorption is not exclusively a material property. There is ashape design component as well. Clearly the greater the cross sectionalarea, the greater the energy required to crush a component with a givenstrength level. This can be overcome by providing a specific energyabsorption, determined by dividing the energy absorbed by the extrudedcomponent's cross sectional area. This still does not define an absolutematerial property, as there are mechanical advantages of some shapedesigns that predispose their ability to absorb more energy than otherdesigns for a given material. In order to overcome these difficultiesand provide an assessment of the material, the energy absorption isexpressed as specific energy absorption (energy absorbed/cross sectionalarea) and is limited to a common crash management component design,which for the purposes of this study, is a three void hollow extrusionwith wall thicknesses from 1.5 mm to 4 mm and a rectangular ortrapezoidal perimeter being 75 mm to 175 mm in the long direction and 40mm to 100 mm in the shorter direction as shown in FIG. 1. Using theseboundaries, materials can be compared even with slightly different shapeconfigurations.

Aluminum extrusions have been utilized in the construction of crashmanagement systems for many years. Successfully attaining a componentthat absorbs energy without fracture, that could threaten injury topassengers, involves complex management of the composition, grainstructure, precipitate structure and mechanical properties. Thecomposition of the extrusions helps to determine the potential strength.In 6XXX alloys under the present invention, precipitation hardeningoccurs with Mg—Si phases (Mg₂Si). The proportion of the Mg and Si (interms of being balanced, excess Si or excess Mg relative to thestoichiometry) can significantly influence the strength and crushperformance as well. The Mg and Si are often assessed in these terms:

Mg/Si Ratio; Calculated by: Mg/(Si−(0.25(Fe+Mn)))

Excess Si; Calculated by: Si−((0.58 Mg)+(Fe+Mn)/4)

Mg₂Si Content; Calculated by:

-   -   if Excess Si is greater than 0 then: 1.58 Mg    -   if Excess Si is less than 0 then: 2.742(Si−((Fe+Mn)/4)))        Additions of Cu also considerably impart strength to the        material. The addition of Sn can also be considered to provide        improved adhesive bond durability to the product, but is not        necessary from an energy absorption perspective. The addition of        Sr can also be considered as it is well known that Sr will        modify the Si phase to a more rounded morphology that will be        less prone to act as a fracture initiation site. Elements such        as Cr and Mn form dispersoids that can be used to retard        recrystallization, thus increasing strength and toughness. These        dispersoids also act as locations to stack-up dislocations,        distributing the matrix dislocation density throughout the        structure and helping to reduce the tendency for void growth,        void consolidation and ultimately fracture. While the        dispersoids retard recrystallization, the thermo-mechanical        process history of the material also plays a major role in        determining the final grain size.

Thus control of processes such as homogenization, billet temperature,use of billet quenches, extrusion die design, extrusion speed and quenchrate post extrusion all play a critical role in the final achieved grainsize in the product. Extrusion of the product can be accomplished byeither a) heating the billet directly to the extrusion temperature or b)using a process referred to as super-heating, where the billet is heatedbeyond the desired extrusion temperature to facilitate the solutionizingof hardening phases, and is then rapidly quenched to desired extrusiontemperature. Both billet heating strategies have been employedsuccessfully in this work. Post extrusion, the material is artificiallyaged to increase its strength. The artificial age time and temperaturecan strongly influence the size, distribution of the precipitateparticles, and even precipitation type in the matrix, which not onlyaffects the potential strength, but can also significantly impact theenergy absorption and crash worthiness of the component. Artificialaging can be delayed to provide an extrusion that has betterformability, with the artificial aging cycle being conducted after thecomponent is formed. In one embodiment, the artificial aging isconducted at billet temperatures between 174-191° C. for 5-10 hours. Theartificial aging can also include multi-step aging to improve corrosionresistance. The artificial aging may be a two-step age cycle with thesecond aging step being hotter than the first aging step and eitheraging step ranging between 100-204° C. In one embodiment, the two-stepage cycles involve a lower temperature step 1 from 100-177° C. and asecond step from 172-204° C. The artificial aging can also intentionallybe under-aged (less than peak strength), with the intention ofsubsequent thermal operations, such as paint baking, completing theremainder of the artificial aging cycle. Alternatively, the component isunaged (T4) to provide better formability of the component withartificial aging being conducted post forming.

All of these factors must be balanced in order to meet multipleobjectives simultaneously. In the case of the present invention, forexample, that is an automotive crash management component with highyield strength and excellent energy absorption without exhibiting atendency for fragmentation. This is achieved with a predominantlyunrecrystallized extruded grain structure in a 6XXX (Al—Mg—Si alloy)hollow extruded material. In a preferred embodiment, the coarse surfacegrain depth is controlled to less than 0.5 mm in depth from the surface.

The following examples illustrate various aspects of the invention andare not intended to limit the scope of the invention.

EXAMPLE 1

Most incumbent alloy compositions used for crash management systems havelower strengths and few dispersoids elements (like Cr and Mn). Thesealloys include 6060 and 6063 for example. The fine recrystallizedstructure attainable in these alloys is known to be preferable forformability and crush applications, although it does not provide thehigher strength levels of other alloys (for example 6082). Alloy 6063has a typical yield strength of 214 MPa and when tested using the crushtest procedures outlined above, only has an energy absorption of 19.468kJ/mm². In an effort to increase the strength and determine theinfluence of Cr as a dispersoid element the compositions in Table 1 werecast, homogenized between 980° F. and 1060° F. (527° C.-566° C.) andthen forced air cooled. Billets from the logs were preheated to 880° F.to 940° F. (471° C.-504° C.), extruded into the three void hollow shapeof FIG. 1 and cold water quenched.

TABLE 1 Composition of Production Cast Billet (weight percent) Cast SiFe Cu Mn Mg Cr Zn Ti 77 0.75 0.26 0.30 0.40 0.74 0.00 0.09 0.03 78 0.730.28 0.29 0.39 0.74 0.19 0.10 0.01

The grain structure of the materials is shown in FIG. 2. The coarsegrain structure resulting from the cast 77 composition resulted infragmentation and excessive cracking and rough deformed surfaces (oftenreferred to as orange peel), while the higher dispersoid content andsubsequent reduced coarse recrystallized grain of cast 78 preventedfragmentation and excessive cracking while also providing a smoothdeformed surface. The differences in deformed surfaces are demonstratedin FIGS. 3 and 4. These results demonstrate the importance ofcontrolling the coarse recrystallized grains with dispersoids in orderto prevent fragmentation, surface cracking and rough deformed surfacesthat precede these unacceptable conditions.

EXAMPLE 2

The composition shown in Table 2 was cast into 10″ (254 mm) diameter logusing development scale equipment.

TABLE 2 Composition of Production Cast Billet (weight percent) Si Fe CuMn Mg Cr Zn Ti 0.66% 0.24% 0.29% 0.40% 0.68% 0.19% 0.04% 0.02%

The logs were homogenized between 980° F. and 1060° F. (527° C.-566° C.)and then forced air cooled. The billets were then extruded into thethree void hollow shape of FIG. 1, described previously, by heating thebillets between 915° F. and 995° F. (491° C.-535° C.) then quenching thebillets to between 730° F. and 925° F. (388° C.-496° C.) prior toextruding and water quenching the resulting extrusions. The extrusionswere stretch straightened/stress relieved and artificially aged between345-375° F. (174-191° C.) for 5-10 hours. Extrusion and artificial agingwas conducted twice, one month apart, to assess reproducibility. Theresulting tensile properties are shown in Table 3.

TABLE 3 Average Mechanical Properties Ultimate Tensile Yield StrengthStrength (0.2% Offset) Elongation Trial Run KSI MPa KSI MPa % 1 44.7 30841.1 284 10.7 2 43 296 39 268 10.8

From both of these extrusion runs, the crash worthiness was assessedwith 100 individual tests throughout the extrusion run. The statisticsof these tests for the specific energy absorption are shown in Table 4.The energy absorption along the length of the extrusion billet is alsoshown in FIG. 5.

TABLE 4 Specific Energy Absorption (kJ/mm²) Average 25.495 Minimum22.843 Maximum 27.412 Standard Deviation 1.053

The qualitative visual examination of these tests were all deemed to beacceptable, meeting the criteria for the tests to be consideredacceptable with no fragmentation or excessive cracking. In addition tothis, the extrusion process parameters were deemed to be acceptable interms of providing consistent results along the extruded length asdemonstrated in FIG. 5.

EXAMPLE 3

Extrusion billet was produced using conventional direct chill castingmethods in 10″ (254 mm) diameter log using production scale equipment tovalidate reproducibility. The composition of this material is shown inTable 5.

TABLE 5 Composition of Production Cast Billet (weight percent) Si Fe CuMn Mg Cr Zn Ti 0.65% 0.29% 0.29% 0.37% 0.60% 0.18% 0.09% 0.03%

The logs were homogenized between 980° F. and 1050° F. (527° C.-566° C.)and then forced air cooled. The billets were then extruded into thethree void hollow shape of FIG. 1, described previously, by heating thebillets between 915° F. and 995° F. (491° C.-535° C.) then quenching thebillets to between 730° F. and 925° F. (388° C.-496° C.) followed byextrusion and water quenching. The extrusions were then stretchstraightened/stress relieved and artificially aged between 345-375° F.(174-191° C.). Billets were extruded in two separate runs to help assurereproducibility. The resulting tensile properties are shown in Table 6.

TABLE 6 Average Mechanical Properties Ultimate Tensile Yield StrengthExtrusion Strength (0.2% Offset) Elongation Run KSI MPa KSI MPa % 1 46.3320 41.9 289 9.48 2 47.3 326 42.6 293 9.92

Samples from the artificially aged material were then tested for crushquality and energy absorption. All samples passed the visual examinationcriteria. The specific energy absorption from this testing is shown inTable 7.

TABLE 7 Specific Energy Absorption Extrusion Run 1 Extrusion Run 2 BothExtrusion Runs Statistic Result (kJ/mm²) Result (kJ/mm²) Result (kJ/mm²)Average 25.658 25.490 25.569 Minimum 24.736 24.634 24.634 Maximum 26.26826.532 26.532 Standard 0.534 0.540 0.536 Deviation

These results demonstrate the repeatability of the process andcompatibility to production scale processes.

EXAMPLE 4

The compositions shown in Table 8 were cast and extruded as per theprevious examples.

TABLE 8 Composition of Production Cast Billet (weight percent) Cast IDSi Fe Cu Mn Mg Cr Zn Ti 1476 CP2 0.57 0.25 0.27 0.40 0.72 0.20 0.05 0.021495 Min 0.57 0.23 0.22 0.40 0.56 0.20 0.05 0.02 1496 Cen 0.65 0.24 0.270.36 0.65 0.16 0.05 0.03 1497 CP1 0.56 0.23 0.27 0.40 0.56 0.20 0.050.03 1498 CP3 0.73 0.23 0.27 0.40 0.55 0.20 0.05 0.03 1499 CP4 0.75 0.230.27 0.40 0.72 0.20 0.05 0.02 1500 Max 0.72 0.24 0.31 0.40 0.73 0.200.05 0.03

The logs were homogenized between 980° F. and 1060° F. (527° C.-566° C.)and then forced air cooled. The billets were then extruded into thethree void hollow shape of FIG. 1, described previously, by heating thebillets between 915° F. and 995° F. (491° C.-535° C.) then quenching thebillets to between 730° F. and 925° F. (388° C.-496° C.) prior toextruding and water quenching the resulting extrusions. The extrusionswere stretch straightened/stress relieved and artificially aged at345-375° F. (174-191° C.) for 5-10 hours.

Samples from all of these materials were tested for mechanicalproperties and tested for energy absorption and crash worthiness. Theresults of this are shown in Tables 9 and 10 and graphically in FIGS.6-8.

TABLE 9 Specific Energy Absorption Results for Example 4 AverageSpecific Minimum Specific Maximum Specific Energy Absorbed EnergyAbsorbed Energy Absorbed Cast (kJ/mm²) (kJ/mm²) (kJ/mm²) 1476 23.7 23.323.9 1495 22.2 22.0 22.5 1496 23.8 22.4 24.7 1497 23.4 23.2 23.5 149825.0 24.7 25.3 1499 25.3 23.6 26.2 1500 25.9 25.5 26.3

TABLE 10 Mechanical Properties of Samples Examined in Example 4 YieldStrength Ultimate Strength (MPa) (MPa) % Elongation Cast Avg Min Max AvgMin Max Avg Min Max 1476 262 261 263 294 291 297 9.9 9.3 10.5 1495 236233 240 268 264 275 10.6 9.7 11.6 1496 283 279 286 308 302 314 9.1 8.99.4 1497 248 244 253 279 274 285 10.1 9.9 10.5 1498 285 284 286 312 311313 9.7 9.3 10.2 1499 299 296 301 325 324 326 9.2 8.8 9.7 1500 300 299300 328 326 329 9.4 9.1 9.8

The specific energy absorption increases with increasing yield strengthand thus the results show that as the amount of solute (as expressed interms of Mg+Si+Cu) the strength and specific energy absorptionincreases. FIG. 6 through 7 show very good correlation coefficientsbetween the simplified solute summation (Mg+Si+(Cu)) as opposed tobreaking it down to the more complex Mg₂Si content and excess Si or Mgas discussed above. Closer examination of the data shows thatcompositions with approximately the same Mg+Si+Cu content (casts 1476,1496, 1498) show benefit from having more excess Si content as opposedto more balanced or closer to excess Mg compositions.

While these results would suggest that specific energy absorption couldbe improved even further with additional solute additions (along withyield strength), it must be noted that with increasing mechanicalproperties, the susceptibility of the material failing from a surfacecracking perspective increases.

EXAMPLE 5

Extrusion billet was produced using conventional direct chill castingmethods in 10″ (254 mm) diameter log using production scale equipment tovalidate reproducibility. The composition of this material is shown inTable 11. The logs were homogenized between 980° F. and 1050° F. (527°C.-566° C.) and then forced air cooled.

TABLE 11 Composition of Production Cast Billet (weight percent) Si Fe CuMn Mg Cr Zn Ti 0.66% 0.27% 0.30% 0.39% 0.63% 0.19% 0.09% 0.02%

Complex extruded shapes can be sensitive to quench rates from theextrusion operation. Faster quench rates can result in dimensionaldistortion that is considered unacceptable for the final application. Itis generally accepted that faster quench rates provide higher strengthsand better resistance to surface cracking during crush testing. In aneffort to determine the alloy sensitivity to quench rate, the three voidhollow shape of FIG. 1 was extruded and immediately cold water sprayquenched using varying water flow rates. The extrusions were stretchstraightened/stress relieved and artificially aged at 345-375° F.(174-191° C.) for 5-10 hours. Samples from all of these materials weretested for mechanical properties, energy absorption and crashworthiness. The results are shown in Table 12.

TABLE 12 Strengths and Energy Absorption at Various Quench Rates QuenchRate Parameter 15 GPM/Zone 21 GPM/Zone 33 GPM/Zone Average UTS (MPa)323.4 330.1 330.1 Average YTS (MPa) 292.2 299.2 298.3 Average %Elongation 10.7 10.7 10.8 Average Energy 27.6 26.6 26.8 Absorption(kJ/mm²)

While the average ultimate and yield strength were slightly lower at thelowest water flow rates studied, the alloy proves to be surprisinglyrobust relative to quench sensitivity from an energy absorptionperspective.

EXAMPLE 6

Complex extruded shapes may be restricted in terms of extrusion speed,with more complex shapes being restricted to slower extrusion speedsthan other shapes. More complex shapes also may require greaterextrusion force. In some cases, the extrusion force may exceed thecapability of the extrusion press and thus higher billet temperaturesare required to enable extrusion of the more complex shapes. In order toassure the alloy was robust in providing consistent mechanicalproperties and energy absorption with these known potential processvariations, billet produced in the same batch of material as in example5 was extruded into the three void hollow shape depicted in FIG. 1 atvarious billet temperatures and extrusion rates. The extrusions werethen cold water quenched, stretch straightened/stress relieved andartificially aged at 345-375° F. (174-191° C.) for 5-10 hours. Samplesfrom all of these materials were tested for mechanical properties,energy absorption and crash worthiness. The results are shown in Table13.

TABLE 13 Strengths and Energy Absorption at Various Extrusion RatesTrial 1 2 3 4 Furnace Billet Temperature 499 499 527 527 (° C.) ExtrudedProduct Speed 3399 7929 3399 7929 (mm/min) Average UTS (MPa) 334.9 337.7331.3 336.1 Average YTS (MPa) 302.0 303.5 301.5 303.8 Average %Elongation 11.7 11.6 10.6 11.0 Average Energy Absorption 26.7 25.6 25.926.1 (kJ/mm²)

The consistency in mechanical properties and energy absorption showsthat this material is also insensitive to both billet temperaturevariation and extrusion rates.

While specific embodiments of the invention have been disclosed, it willbe appreciated by those skilled in the art that various modificationsand alterations to those details could be developed in light of theoverall teachings of the disclosure. Accordingly, the particulararrangements disclosed are meant to be illustrative only and notlimiting as to the scope of the invention which is to be given the fullbreadth if the appended claims and any and all equivalents thereof.

1. An energy absorption extrusion component produced from an alloycomposition comprising, in weight percent, Si: 0.50-0.80; Fe: <0.40; Cu:0.15-0.35; Mn: 0.20-0.50; Mg: 0.50-0.80; Cr: 0.10-0.25; Zn: <0.20; withother elements being considered incidental elements and consisting ofless than 0.05 individually and 0.15 in total with the balance beingaluminum
 2. The component of claim 1 wherein said extrusion componenthas a specific energy absorption of greater than 22 kJ/mm² and a yieldstrength of greater than 260 MPa while providing no fragmentation orsurface cracks greater than 10 mm during defined crush testing wherein a300 mm long sample is crushed in the longitudinal direction to 100 mm ata rate of 100 mm/minute.
 3. The component of claim 1, wherein saidextrusion component has a yield strength greater than 280 MPa.
 4. Thecomponent of claim 1 wherein said extrusion component has a specificenergy absorption of greater than 22 kJ/mm² and a yield strength greaterthan 280 MPa with no fragmentation or surface crack greater than 20 mmduring defined crush testing wherein a 300 mm long sample is crushed inthe longitudinal direction to 100 mm at a rate of 100 mm/minute.
 5. Thecomponent of claim 1 wherein said extrusion component has a specificenergy absorption of greater than 22 kJ/mm² and a yield strength greaterthan 300 MPa with no fragmentation or surface crack greater than 30 mmduring defined crush testing wherein a 300 mm long sample is crushed inthe longitudinal direction to 100 mm at a rate of 100 mm/minute.
 6. Thecomponent of claim 1 wherein said alloy composition further comprises Snthat is intentionally added at levels of 0.02-0.10% by weight.
 7. Thecomponent of claim 1 wherein said alloy composition further comprises Srthat is intentionally added at levels up to 0.30% by weight.
 8. Thecomponent of claim 1 wherein said alloy composition further comprises Vthat is not intentionally added.
 9. The component of claim 1 whereinsaid alloy composition further comprises V ≤0.04% by weight.
 10. Thecomponent of claim 1 used as an automotive crush can, front rail, rearrail, upper rail, rocker, header, A-pillar, or roof rail.
 11. A methodfor making the extrusion component of claim 1 comprising, i)homogenizing a billet including said alloy composition at a billettemperature between 527-566° C., ii) followed by fan cooling, iii)followed by either a) extruding with a billet temperature between 455°C. to 510° C. or b) heating to a billet temperature of 491° C.-535° C.,then water quenching to a billet temperature of 388° C.-496° C., andthen extruding, iv) followed by cold water quenching; stretching; andartificial aging wherein the extrusion component has a specific energyabsorption of greater than 22 kJ/mm² and a yield strength of greaterthan 260 MPa while providing no fragmentation or surface cracks greaterthan 10 mm during defined crush testing wherein a 300 mm long sample iscrushed in the longitudinal direction to 100 mm at a rate of 100mm/minute.
 12. The method of claim 11, wherein the billet is initiallyheated to 491° C.-535° C., then water quenched to a temperature of 388°C.-496° C. prior to extruding.
 13. The method of claim 11, wherein thebillet is extruding with a billet temperature between 455° C. to 510° C.after fan cooling
 14. The method of claim 11 wherein said extrusioncomponent has a coarse surface grain depth that is controlled to lessthan 0.5 mm in depth from the surface.
 15. The method of claim 11wherein the artificial aging is conducted using a two-step cycle with asecond aging step being hotter than a first aging step and either agingsteps ranging between 100-204° C.
 16. The method of claim 15, whereinthe two-step age cycle involves a first aging step from 100-177° C. anda second aging step from 172-204° C.
 17. The method of claim 11 whereinthe artificial aging is conducted at a billet temperature between174-191° C. for 5-10 hours.
 18. The method of claim 11 wherein saidcomponent is provided in an unaged (T4) condition with artificial agingconducted post forming.
 19. The method of claim 11 wherein saidcomponent is provided in an under-aged condition with the remaining peakage strengthening accomplished during subsequent thermal operations.